This invention relates to a process for fortifying the sulfuric acid catalyst used as an alkylation catalyst in the production of premium grade (high octane number) gasoline by the petroleum industry. More particularly, this invention relates to the periodic fortification of the alkylation acid to increase the octane rating of the product alkylate and to prolong the catalytic effectiveness of the sulfuric acid.
It is common practice in petroleum refineries to treat low boiling isoparaffins or alkanes with alkylating reagents such as olefins, in the presence of a sulfuric acid catalyst to produce a high octane alkylate, boiling in the gasoline range. It is well know that the sulfuric acid catalyst does not undergo major chemical change during the alkylation process but the acid concentration diminishes due to the build-up of water and organic impurities and red oils which originate from undesired side reactions. As the build-up of these diluents approaches 10-12%, the concentration of the alkylation acid is reduced from its original value of about 98.0-99.5% to about 88-90%. At these lower concentration values, the catalytic activity of the alkylation acid is decreased and the octane number of the product alkylate is undesirably lower. At this point all the alkylation acid must be withdrawn from the system and reprocessed by regeneration. In reprocessing, the spent acid is usually thermally decomposed to sulfur dioxide, carbon dioxide and water. After purification, the sulfur dioxide generated is reconverted to sulfuric acid by the conventional contact process.
Besides the fuel and energy required to regenerate the acid, another obvious disadvantage of this widely used destructive regeneration process is that the spent acid, consisting mostly (88-90%) of sulfuric acid, is completely decomposed to eliminate the relatively small amounts (10-12%) of water and organic impurities. Analyses of spent or used alkylation acid vary somewhat depending on the operating conditions.